1. Field of the Invention
The present invention relates to a roll profile measuring system for measuring a roll profile of a work roll assembled in a rolling mill and a measuring method using the system, and particularly to an online roll profile measuring system suitable for measuring a roll profile of a work roll during rolling and a measuring method using the system.
2. Description of the Related Art
In general, when work rolls assembled in a rolling mill are used for rolling a material to be rolled at a high rolling force, they are reduced in diameter locally only at portions between which the material passes by the effect of thermal expansion and/or wearing. Conventionally, a roll profile of a work roll has been calculated by a computer using measured data on thermal expansion and/or wearing of the work roll.
Such a method, however, has failed to obtain a high measurement accuracy, and therefore, various methods of measuring an actual roll profile during rolling have been proposed.
For example, one actual roll profile measuring method has been disclosed in a document entitled "Long Life Online Roll Grinder Aimed at Improvement in Productivity": Hitachi Review, Vol. 75 (June, 1993). In this method, a roll profile is calculated, simultaneously with grinding of a work roll, on the basis of data on a contact force between a rotary grinding wheel and the work roll, spring constant of the rotary grinding wheel, and pressing position of the rotary grinding wheel and movement position of a traversing device upon grinding. Hereinafter, this method is referred to as "a first method".
Another actual roll profile measuring method has been disclosed in Japanese Patent Laid-open No. Sho 59-156508. In this method, vibration generated during rotation of a work roll is regarded as a main cause of a measurement error of a roll profile. Specifically, sensors for measuring a movement amount of a work roll due to looseness at two portions of an end portion of the work roll in the X and Y directions are provided on a work roll profile measuring frame, and a mark is provided on the outer periphery of the work roll for measuring the rotating angle of the work roll, wherein the mark is measured by the sensors fixed on the frame. Hereinafter, this method is referred to as "a second method".
The first method is allowed to actually measure a roll profile in a condition that a distance between the work roll and a guide rail for moving a roll grinder unit containing the rotary grinding wheel in the axial direction of the work roll remains unchanged. Specifically, in this method, since the roll profile of the work roll is measured during idling in which the rolling condition is not changed, a housing is not deformed and/or the work roll is not moved in the vertical direction due to the change in strip thickness. As a result, the online roll profile of the work roll can be calculated by eliminating, from the state of the work roll before rolling, the changed amount of the work roll due to wearing and/or thermal expansion caused by rolling.
In a rolling mill, there exists an idling time of work rolls from at the time when a material is thinly rolled to the time when the next material is bitten in the rolling mill. The roll profile of a work roll may be measured by making use of the idling time. Specifically, for such an idling time, the work roll is ground at a specific pressing force and simultaneously the roll profile is calculated on the basis of movement amounts of a pressing device and a traversing device. This makes it possible to obtain an accurate roll profile because the rolling condition is not changed for the idling time.
However, with an increase in productivity, the idling time tends to be shortened, and thereby it becomes difficult to grind the entire length of a work roll for the idling time. For this reason, it is required to measure an accurate roll profile of a work roll simultaneously with grinding of the work roll during rolling.
In the case where a work roll is ground in a state that the online roll grind unit is fixed on a housing, since the housing is deformed due to the change in rolling condition during rolling, the distance between the guide rail and the work roll is slightly changed. As a result, there occurs a problem that the roll profile of the work roll measured simultaneously with grinding of the work roll during rolling contains not only the changed amount of the work roll based on the state before rolling due to the thermal effect and/or wearing caused by rolling but also an error due to displacement of the housing caused by the change in rolling condition during rolling, that is, the change in distance between the guide rail and the work roll.
Incidentally, since the work roll is rotated in chocks, there occurs a run-out of the rotating work roll by the presence of gaps between the chocks and bearings and gaps in the bearings. To prevent occurrence of measurement errors of the roll profile due to the run-out of the work roll and the eccentricity of the work roll, according to the above-described second method, there is provided the sensor for measuring the rotational position of the work roll and the amount of run-out of the work roll.
The run-out and eccentricity of the work roll, however, can be electrically processed without provision of the sensor because the amount of run-out of the work roll can be made constant by increasing the rotational speed of the work roll. And, the second method fails to solve the above-described problem that the roll profile of the work roll measured simultaneously with grinding of the work roll during rolling contains an error due to displacement of the housing caused by the change in rolling condition during rolling, that is, the change in distance between the guide rail and the work roll during rolling.